Magnetic resonance tomography (MRT) enables sectional images (slices) of the human (or animal) body to be generated that permit an assessment of the organs and many pathological organ changes. MRT is based on very strong magnetic fields, generated in a magnetic resonance tomography (MRT) system, as well as on alternating magnetic fields in the radio frequency range by which specific atomic nuclei (mostly the hydrogen nuclei/protons) in the body are excited into resonance, thereby inducing an electrical signal in a receiver circuit.
MRT systems may be installed as stationary appliances. It is, however, also possible to install mobile MRT systems for example on trailers of heavy-duty motorized tractor vehicles, which may then be brought to the respective deployment location. Such mobile MRT systems require a stray magnetic field shield made of iron. Due to the constricted space conditions in trailers, the shield extends by reason of construction-related constraints two-dimensionally in the vertical walls over an area of approximately 30 m2 and is closer to the magnets of the MRT system and less insulated from the outside world than in the case of stationary installations.
Since mobile MRT systems may be set up in the open, changing weather conditions lead to spatially and temporally widely varying amounts of heat being introduced into the iron shield. The change in temperature of the iron leads to a change in the susceptibility of the iron and consequently to a change in magnetization. This disrupts the homogeneity of the static magnetic field of the MRT system. Furthermore, the shielding iron expands as a result of its being heated, which likewise affects the homogeneity of the static magnetic field. Frequency shifts and image quality limitations during the MRT examination are the consequence.
Efforts have thus far been directed at attempting to realize a mounting of the iron shield that is largely decoupled mechanically and thermally from the trailer. Given a typical weight of several metric tons, this is problematic and only achievable with compromises. For this reason, additional heat insulation is normally provided in the external walls of the trailer to act as a thermal shield, e.g., in the form of panels made of synthetic organic foams having the lowest possible coefficient of heat transmission. In this case, however, consideration is given to the amount of space available. Therefore, the desired heat insulation is in contention with space requirements in the trailer as well as with the permissible external dimensions.